Van De Graaff Generators & High Voltage Stuff
Since becoming interested in building VDG machines, I have learnt a great deal. Much time has been spent searching for the best material combination for the rollers and belt and this is still an ongoing process. There was also the unexpected learning process re-educating myself as to what materials are good insulators and what aren' t! At these voltage levels, certain plastics and rubbers are actually very poor insulators and you don' t want to build a VDG out of these! So in order to produce the best results, select the materials for the upper and lower rollers that are as far apart on the Triboelectric Series as possible.
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Asbestos

Glass

Nylon

Wool

Lead

Silk

Aluminium

Paper

Cotton

Steel

Hard Rubber

Nickel & copper

brass & silver

synthetic rubber

orlon

saran

polyethylene

teflon

silicone rubber

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The series above should only be used as a guide. The effectiveness of a material to hold charge will vary with its composition and its purity The position of a material within the series, only indicates its effectiveness relative to other materials in the series. It does not give any indication as to the magnitude of that ability. Cleanliness is also very important. Any surface contamination such as grease deposits will reduce the surface area available for charge transfer or will increase the amount of unwanted leakage, resulting in less than optimum performance. Avoid materials that have an open structure i.e. hygroscopic, as these will be subject to extremely variable performance ranging from poor to useless depending on humidity levels. Also beware of materials such as glass. Although generally an excellent insulator, it will support condensation on its surface when subject to temperature differentials. Moisture is one of your biggest enemies when building VDG machines. As with most engineering problems, the optimum solution is generally a compromise. The art is in finding the correct level of compromise to suit the performance target.

Last update 10/02/03